Last Updated Mar 26, 2015 11:01 PM EDT
NEW YORK -- At least 19 people were injured, four of them critically, when a gas explosion ripped through four buildings in New York City's East Village, Mayor Bill de Blasio and fire officials said Thursday.
The explosion was reported at around 3:17 p.m. at 7th Street and Second Avenue. Fire crews were on the scene within three minutes, according to FDNY Commissioner Daniel Nigro.
"It was very quick; it was very instantaneous -- kaboom," a witness told CBS New York reporter Valerie Castro.
Restaurant diners ran out of their shoes and bystanders helped one another to escape the midafternoon blast, which damaged four buildings as flames shot scores of feet into the air, witnesses said.
Passers-by were hit by debris and flying glass, and bloodied victims were aided as they sat on sidewalks and lay on the ground, they said.
"It was terrifying -- absolutely terrifying," said Bruce Finley, a visitor from San Antonio, Texas, who had just taken a photo of his order at a restaurant known for its French fries when he felt the explosion next door. "It just happened out of the blue. ... We were shaking even an hour, hour and a half later."
The explosion occurred in a five-story residential and commercial building on Second Avenue, not far from New York University. The fire escalated to seven alarms within an hour of the explosion with about 250 firefighters on scene, according to the FDNY.
By late Thursday, at least two of the buildings had collapsed and the others were unstable, according to fire officials. An FDNY video captured one of the buildings falling down as firefighters attempted to extinguis the flames.
Fire officials said 14 of the people who were hurt are civilians and five are firefighters. Seven people suffered minor injuries, and four were treated at the scene.
"Our thoughts and prayers are with every one of them and their families. Of course, we are praying that no other individuals are injured and there are no fatalities," de Blasio said.
Preliminary evidence suggested a gas explosion amid plumbing and gas work inside the first building that collapsed was to blame, de Blasio said.
A plumber was doing work connected to a gas service upgrade, and inspectors from utility Con Edison had been there to check on a planned meter installation about an hour before the fire, company President Craig Ivey said.
But the work failed the inspection, partly because a space for the new meters wasn't big enough, and the inspectors said gas couldn't be introduced to that part of the building, Con Ed said.
De Blasio noted that no one had reported a gas leak to authorities before Thursday's blast.
"If people smell gas, they should immediately call 911 or Con Edison," de Blasio said. "That's the one thing we know for sure."
Con Edison said it had surveyed all the gas mains on the block Wednesday and found no leaks. The state Department of Public Service was monitoring Con Ed's response.
According to the New York Buildings Department, there was a stop-work order on the building where the blast occurred.
Freelance photographer Michael Seto, who lives about 1 1/2 blocks away, told the Associated Press he was having lunch around 3:20 p.m. "I could feel the boom in my apartment, and it short of shook," Seto said.
He grabbed his camera, ran outside and found a crowd gathering, looking at a brick tenement-style building with a restaurant on the first floor.
"By the second story, the front part of the building, the facade, the first and second stories, it looked like, had collapsed into the street," he said. Rubble was on the sidewalk, and glass and debris had been flung across an avenue.
As Seto ran up to the building, a fire was starting inside it. "It spread very quickly and pretty much engulfed the first floor," he said.
Firefighters and investigators remained at the scene late Thursday night. It was unclear when residents and workers who lived and worked in nearby buildings would be allowed to return.
The American Red Cross of Greater New York, which established a shelter at P.S. 63, said a total of 49 residential units were affected by the explosion, CBS New York reported.
There was a large volume of smoke in the area after the blast and fire. Police handed out masks to people in the area as officials told residents to keep their windows shut.
The city's Department of Environmental Protection was determining the environmental and health impact of the explosion, de Blasio said. The New York City Department of Health and Mental Hygiene also set up a website on the health risks related to smoke from the explosion.
The blast and fire come just over a year after a major building explosion in Harlem killed eight people, injured at least 60 others and collapsed two buildings.
A National Transportation Safety Board investigation determined a gas main leaked prior to the Harlem explosion and had not been pressure-tested because of a New York State exemption, CBS New York reported.